bteSERVATioNS Foil Time and longitude. 173 
of the parallax. The length of AD is found on actual measurement to 
equal °f the radius FC of the circle; so that— 
Parallax = x \fo x horizontal parallax 
- * x 59' 16" 
= 8' 48" 
Were the declination south instead of north, the parallax Would be 
^presented by AD'; this equals T 4 o 9 o of the radius, and the parallax would 
equal— 
t % 9 0 x 59' 16" = 29' 0" 
In some cases the hour angle may exceed six hours, and the line of the 
moon’s declination may require to be produced through C; for instance* 
the line EF represents the parallax in declination under the conditions— 
latitude, 45° N.; hour angle, 6h. 45m.; declination, 30° S. 
Sign of the Parallax in Declination .—If the place of observation as 
plotted in the diagram is below the line drawn through the centre and 
the declination, the effect of the parallax will obviously be to move 
apparently the position of the moon towards the north; it will thus 
increase north and decrease south declination. The converse is also 
true. Thus, in the first example the parallax represented by AD would 
be added to the moon’s north declination; that by AD' would be added 
to the moon’s south declination; and that by EF would be added to the 
moon’s south declination. 
Parallax in Bight Ascension . 
The diagram now represents a similar projection on a vertical plane at 
right angles to the former, and the hour angles should be plotted from 
the vertical line passing through the centre of the circle, and counted as 
numbered in the upper series of figures. If from the point plotted by 
latitude and hour angle a perpendicular line be drawn to the centre 
Vertical line, the length of this perpendicular is a measure of the parallax; 
but instead of being, in all cases, measured on the radius of F C of the 
circle, as in finding the parallax in declination, it should be measured on 
the scale of the radius of that declination circle representing the moon’s 
declination. These radii for declinations from 0° to 32°, which covers the 
